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Li X, Wang Y, Deng S, Zhu G, Wang C, Johnson NA, Zhang Z, Tirado CR, Xu Y, Metang LA, Gonzalez J, Mukherji A, Ye J, Yang Y, Peng W, Tang Y, Hofstad M, Xie Z, Yoon H, Chen L, Liu X, Chen S, Zhu H, Strand D, Liang H, Raj G, He HH, Mendell JT, Li B, Wang T, Mu P. Loss of SYNCRIP unleashes APOBEC-driven mutagenesis, tumor heterogeneity, and AR-targeted therapy resistance in prostate cancer. Cancer Cell 2023; 41:1427-1449.e12. [PMID: 37478850 PMCID: PMC10530398 DOI: 10.1016/j.ccell.2023.06.010] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/02/2022] [Revised: 05/24/2023] [Accepted: 06/29/2023] [Indexed: 07/23/2023]
Abstract
Tumor mutational burden and heterogeneity has been suggested to fuel resistance to many targeted therapies. The cytosine deaminase APOBEC proteins have been implicated in the mutational signatures of more than 70% of human cancers. However, the mechanism underlying how cancer cells hijack the APOBEC mediated mutagenesis machinery to promote tumor heterogeneity, and thereby foster therapy resistance remains unclear. We identify SYNCRIP as an endogenous molecular brake which suppresses APOBEC-driven mutagenesis in prostate cancer (PCa). Overactivated APOBEC3B, in SYNCRIP-deficient PCa cells, is a key mutator, representing the molecular source of driver mutations in some frequently mutated genes in PCa, including FOXA1, EP300. Functional screening identifies eight crucial drivers for androgen receptor (AR)-targeted therapy resistance in PCa that are mutated by APOBEC3B: BRD7, CBX8, EP300, FOXA1, HDAC5, HSF4, STAT3, and AR. These results uncover a cell-intrinsic mechanism that unleashes APOBEC-driven mutagenesis, which plays a significant role in conferring AR-targeted therapy resistance in PCa.
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Affiliation(s)
- Xiaoling Li
- Department of Molecular Biology, UT Southwestern Medical Center, Dallas, TX, USA
| | - Yunguan Wang
- Quantitative Biomedical Research Center, Peter O'Donnell Jr. School of Public Health, UT Southwestern Medical Center, Dallas, TX, USA; Division of Biomedical Informatics, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, USA
| | - Su Deng
- Department of Molecular Biology, UT Southwestern Medical Center, Dallas, TX, USA
| | - Guanghui Zhu
- Department of Medical Biophysics, University of Toronto, Toronto, ON, Canada; Princess Margaret Cancer Center, University Health Network, Toronto, ON, Canada
| | - Choushi Wang
- Department of Molecular Biology, UT Southwestern Medical Center, Dallas, TX, USA
| | - Nickolas A Johnson
- Department of Molecular Biology, UT Southwestern Medical Center, Dallas, TX, USA
| | - Zeda Zhang
- Human Oncology and Pathogenesis Program, Memorial Sloan Kettering Cancer Center, New York, NY, USA
| | | | - Yaru Xu
- Department of Molecular Biology, UT Southwestern Medical Center, Dallas, TX, USA
| | - Lauren A Metang
- Department of Molecular Biology, UT Southwestern Medical Center, Dallas, TX, USA
| | - Julisa Gonzalez
- Department of Molecular Biology, UT Southwestern Medical Center, Dallas, TX, USA
| | - Atreyi Mukherji
- Department of Molecular Biology, UT Southwestern Medical Center, Dallas, TX, USA
| | - Jianfeng Ye
- Lyda Hill Department of Bioinformatics, UT Southwestern Medical Center, Dallas, TX, USA
| | - Yuqiu Yang
- Quantitative Biomedical Research Center, Peter O'Donnell Jr. School of Public Health, UT Southwestern Medical Center, Dallas, TX, USA
| | - Wei Peng
- Department of Molecular Biology, UT Southwestern Medical Center, Dallas, TX, USA
| | - Yitao Tang
- Department of Bioinformatics and Computational Biology, MD Anderson Cancer Center, Houston, TX, USA
| | - Mia Hofstad
- Department of Urology, UT Southwestern Medical Center, Dallas, TX, USA
| | - Zhiqun Xie
- Quantitative Biomedical Research Center, Peter O'Donnell Jr. School of Public Health, UT Southwestern Medical Center, Dallas, TX, USA
| | - Heewon Yoon
- Department of Molecular Biology, UT Southwestern Medical Center, Dallas, TX, USA
| | - Liping Chen
- Department of Urology, UT Southwestern Medical Center, Dallas, TX, USA
| | - Xihui Liu
- Department of Urology, UT Southwestern Medical Center, Dallas, TX, USA
| | - Sujun Chen
- Department of Medical Biophysics, University of Toronto, Toronto, ON, Canada; Princess Margaret Cancer Center, University Health Network, Toronto, ON, Canada
| | - Hong Zhu
- Quantitative Biomedical Research Center, Peter O'Donnell Jr. School of Public Health, UT Southwestern Medical Center, Dallas, TX, USA; Harold C. Simmons Comprehensive Cancer Center, UT Southwestern Medical Center, Dallas, TX, USA
| | - Douglas Strand
- Department of Urology, UT Southwestern Medical Center, Dallas, TX, USA; Harold C. Simmons Comprehensive Cancer Center, UT Southwestern Medical Center, Dallas, TX, USA
| | - Han Liang
- Department of Bioinformatics and Computational Biology, MD Anderson Cancer Center, Houston, TX, USA; Department of Systems Biology, MD Anderson Cancer Center, Houston, TX, USA
| | - Ganesh Raj
- Department of Urology, UT Southwestern Medical Center, Dallas, TX, USA; Harold C. Simmons Comprehensive Cancer Center, UT Southwestern Medical Center, Dallas, TX, USA
| | - Housheng Hansen He
- Department of Medical Biophysics, University of Toronto, Toronto, ON, Canada; Princess Margaret Cancer Center, University Health Network, Toronto, ON, Canada
| | - Joshua T Mendell
- Department of Molecular Biology, UT Southwestern Medical Center, Dallas, TX, USA; Harold C. Simmons Comprehensive Cancer Center, UT Southwestern Medical Center, Dallas, TX, USA; Howard Hughes Medical Institute, Chevy Chase, MD, USA; Hamon Center for Regenerative Science and Medicine, UT Southwestern Medical Center, Dallas, TX, USA
| | - Bo Li
- Lyda Hill Department of Bioinformatics, UT Southwestern Medical Center, Dallas, TX, USA
| | - Tao Wang
- Quantitative Biomedical Research Center, Peter O'Donnell Jr. School of Public Health, UT Southwestern Medical Center, Dallas, TX, USA
| | - Ping Mu
- Department of Molecular Biology, UT Southwestern Medical Center, Dallas, TX, USA; Harold C. Simmons Comprehensive Cancer Center, UT Southwestern Medical Center, Dallas, TX, USA; Hamon Center for Regenerative Science and Medicine, UT Southwestern Medical Center, Dallas, TX, USA.
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2
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RNA binding motif 47 (RBM47): emerging roles in vertebrate development, RNA editing and cancer. Mol Cell Biochem 2021; 476:4493-4505. [PMID: 34499322 DOI: 10.1007/s11010-021-04256-5] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2021] [Accepted: 08/31/2021] [Indexed: 10/20/2022]
Abstract
RNA-binding proteins (RBPs) are critical players in the post-transcriptional regulation of gene expression and are associated with each event in RNA metabolism. The term 'RNA-binding motif' (RBM) is assigned to novel RBPs with one or more RNA recognition motif (RRM) domains that are mainly involved in the nuclear processing of RNAs. RBM47 is a novel RBP conserved in vertebrates with three RRM domains whose contributions to various aspects of cellular functions are as yet emerging. Loss of RBM47 function affects head morphogenesis in zebrafish embryos and leads to perinatal lethality in mouse embryos, thereby assigning it to be an essential gene in early development of vertebrates. Its function as an essential cofactor for APOBEC1 in C to U RNA editing of several targets through substitution for A1CF in the A1CF-APOBEC1 editosome, established a new paradigm in the field. Recent advances in the understanding of its involvement in cancer progression assigned RBM47 to be a tumor suppressor that acts by inhibiting EMT and Wnt/[Formula: see text]-catenin signaling through post-transcriptional regulation. RBM47 is also required to maintain immune homeostasis, which adds another facet to its regulatory role in cellular functions. Here, we review the emerging roles of RBM47 in various biological contexts and discuss the current gaps in our knowledge alongside future perspectives for the field.
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3
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Yang Y, Chen Q, Piao HY, Wang B, Zhu GQ, Chen EB, Xiao K, Zhou ZJ, Shi GM, Shi YH, Wu WZ, Fan J, Zhou J, Dai Z. HNRNPAB-regulated lncRNA-ELF209 inhibits the malignancy of hepatocellular carcinoma. Int J Cancer 2019; 146:169-180. [PMID: 31090062 DOI: 10.1002/ijc.32409] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2019] [Revised: 04/20/2019] [Accepted: 05/02/2019] [Indexed: 01/01/2023]
Abstract
Our previous study demonstrated that heterogeneous nuclear ribonucleoprotein AB (HNRNPAB) is a key gene that facilitates metastasis of hepatocellular carcinoma (HCC). However, the molecular mechanisms behind this relationship are not fully understood. In our study, we utilized long-noncoding RNA (lncRNA) microarrays to identify a HNRNPAB-regulated lncRNA named lnc-ELF209. Our findings from chromatin immunoprecipitation assays indicate that HNRNPAB represses lnc-ELF209 transcription by directly binding to its promoter region. We also analyzed clinical samples from HCC patients and cell lines with quantitative real-time polymerase chain reactions, RNA in situ hybridization and immunohistochemistry, and found that there is a negative relationship between HNRNPAB and lnc-ELF209 expression. Up/downregulation assays and rescue assays indicate that lnc-ELF209 inhibits cell migration, invasion and epithelial-mesenchymal transition regulated by HNRNPAB. This suggests a new regulatory mechanism for HNRNPAB-promoted HCC progression. RNA pull-down and LC-MS/MS were used to determine triosephosphate isomerase, heat shock protein 90-beta and vimentin may be involved in the tumor-suppressed function of lnc-ELF209. Furthermore, we found lnc-ELF209 could stabilize TPI protein expression. We also found that lnc-ELF209 overexpression in HCCLM3 cell resulted in a lower rate of lung metastatic, which suggested a less aggressive HCC phenotype. Collectively, these findings offer new insights into the regulatory mechanisms that underlie HNRNPAB cancer-promoting activities and demonstrate that lnc-ELF209 is a HNRNPAB-regulated lncRNA that may play an important role in the inhibition of HCC progression.
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Affiliation(s)
- Yi Yang
- Liver Cancer Institute, Zhongshan Hospital, Fudan University, Shanghai, China.,State Key Laboratory of Genetic Engineering, Fudan University, Shanghai, China.,Key Laboratory of Carcinogenesis and Cancer Invasion, Fudan University, Ministry of Education, Shanghai, China
| | - Qing Chen
- Department of General Surgery, Zhongshan Hospital (South), Fudan University, Shanghai Public Health Clinical Center, Fudan University, Shanghai, China
| | - Hai-Yan Piao
- Medical Oncology Department of Gastrointestinal cancer, Cancer Hospital of China Medical University, Liaoning Cancer Hospital & Institute, Shenyang, China
| | - Biao Wang
- Liver Cancer Institute, Zhongshan Hospital, Fudan University, Shanghai, China.,State Key Laboratory of Genetic Engineering, Fudan University, Shanghai, China.,Key Laboratory of Carcinogenesis and Cancer Invasion, Fudan University, Ministry of Education, Shanghai, China
| | - Gui-Qi Zhu
- Liver Cancer Institute, Zhongshan Hospital, Fudan University, Shanghai, China.,State Key Laboratory of Genetic Engineering, Fudan University, Shanghai, China.,Key Laboratory of Carcinogenesis and Cancer Invasion, Fudan University, Ministry of Education, Shanghai, China
| | - Er-Bao Chen
- Liver Cancer Institute, Zhongshan Hospital, Fudan University, Shanghai, China.,State Key Laboratory of Genetic Engineering, Fudan University, Shanghai, China.,Key Laboratory of Carcinogenesis and Cancer Invasion, Fudan University, Ministry of Education, Shanghai, China
| | - Kun Xiao
- Liver Cancer Institute, Zhongshan Hospital, Fudan University, Shanghai, China.,State Key Laboratory of Genetic Engineering, Fudan University, Shanghai, China.,Key Laboratory of Carcinogenesis and Cancer Invasion, Fudan University, Ministry of Education, Shanghai, China
| | - Zheng-Jun Zhou
- Liver Cancer Institute, Zhongshan Hospital, Fudan University, Shanghai, China.,State Key Laboratory of Genetic Engineering, Fudan University, Shanghai, China.,Key Laboratory of Carcinogenesis and Cancer Invasion, Fudan University, Ministry of Education, Shanghai, China
| | - Guo-Ming Shi
- Liver Cancer Institute, Zhongshan Hospital, Fudan University, Shanghai, China.,State Key Laboratory of Genetic Engineering, Fudan University, Shanghai, China.,Key Laboratory of Carcinogenesis and Cancer Invasion, Fudan University, Ministry of Education, Shanghai, China
| | - Ying-Hong Shi
- Liver Cancer Institute, Zhongshan Hospital, Fudan University, Shanghai, China.,State Key Laboratory of Genetic Engineering, Fudan University, Shanghai, China.,Key Laboratory of Carcinogenesis and Cancer Invasion, Fudan University, Ministry of Education, Shanghai, China
| | - Wei-Zhong Wu
- Liver Cancer Institute, Zhongshan Hospital, Fudan University, Shanghai, China.,State Key Laboratory of Genetic Engineering, Fudan University, Shanghai, China.,Key Laboratory of Carcinogenesis and Cancer Invasion, Fudan University, Ministry of Education, Shanghai, China
| | - Jia Fan
- Liver Cancer Institute, Zhongshan Hospital, Fudan University, Shanghai, China.,State Key Laboratory of Genetic Engineering, Fudan University, Shanghai, China.,Key Laboratory of Carcinogenesis and Cancer Invasion, Fudan University, Ministry of Education, Shanghai, China
| | - Jian Zhou
- Liver Cancer Institute, Zhongshan Hospital, Fudan University, Shanghai, China.,State Key Laboratory of Genetic Engineering, Fudan University, Shanghai, China.,Key Laboratory of Carcinogenesis and Cancer Invasion, Fudan University, Ministry of Education, Shanghai, China
| | - Zhi Dai
- Liver Cancer Institute, Zhongshan Hospital, Fudan University, Shanghai, China.,State Key Laboratory of Genetic Engineering, Fudan University, Shanghai, China.,Key Laboratory of Carcinogenesis and Cancer Invasion, Fudan University, Ministry of Education, Shanghai, China
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4
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Jung Y, Ryu HG, Kim SW, Lee KH, Gu S, Yi H, Ku HO, Jang SK, Kim KT. The RNA-binding protein hnRNP Q represses translation of the clock gene Bmal1 in murine cells. J Biol Chem 2019; 294:7682-7691. [PMID: 30948510 PMCID: PMC6514626 DOI: 10.1074/jbc.ra118.006947] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2018] [Revised: 03/28/2019] [Indexed: 11/06/2022] Open
Abstract
Most living creatures have a circadian rhythm that is generated by a precisely regulated transcriptional-translational feedback loop of clock genes. Brain and muscle ARNT-like 1 (BMAL1) is one of the core clock genes and transcription factors that represents a positive arm of this autoregulatory circadian clock system. Despite the indispensable role of BMAL1 in the circadian rhythm, the molecular mechanisms underlying translational control of BMAL1 are largely unknown. Here, using murine NIH-3T3 cells, gene constructs, and a variety of biochemical approaches, including RNAi- and luciferase reporter gene-based assays, along with immunoblotting, in vitro transcription, quantitative real-time PCR, and real-time bioluminescence experiments, we show that translation of Bmal1 is negatively regulated by an RNA-binding protein, heterogeneous nuclear ribonucleoprotein Q (hnRNP Q). Interestingly, we found that hnRNP Q rhythmically binds to a specific region of the Bmal1 mRNA 5' UTR and controls its time-dependent expression. Moreover, we demonstrate that knockdown of hnRNP Q modulates BMAL1 protein oscillation amplitude without affecting mRNA rhythmic patterns. Furthermore, hnRNP Q depletion increases the mRNA oscillation amplitudes of BMAL1-regulated target genes. Together, our results suggest that hnRNP Q plays a pivotal role in both Bmal1 translation and BMAL1-regulated gene expression.
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Affiliation(s)
- Youngseob Jung
- From the Division of Integrative Biosciences and Biotechnology and
| | - Hye Guk Ryu
- Department of Life Sciences, Pohang University of Science and Technology, Pohang, Gyeongbuk 37673, Republic of Korea
| | - Sung Wook Kim
- From the Division of Integrative Biosciences and Biotechnology and
| | - Kyung-Ha Lee
- the Division of Cosmetic Science and Technology, Daegu Haany University, Gyeongsan, Gyeongbuk 38610, Republic of Korea, and
| | - Sohyun Gu
- Department of Life Sciences, Pohang University of Science and Technology, Pohang, Gyeongbuk 37673, Republic of Korea
| | - Hee Yi
- the Vet Drugs and Biologics Division, Animal and Plant Quarantine Agency, Gimcheon, Gyeongbuk 39660, Republic of Korea
| | - Hyun-Ok Ku
- the Vet Drugs and Biologics Division, Animal and Plant Quarantine Agency, Gimcheon, Gyeongbuk 39660, Republic of Korea
| | - Sung Key Jang
- Department of Life Sciences, Pohang University of Science and Technology, Pohang, Gyeongbuk 37673, Republic of Korea
| | - Kyong-Tai Kim
- From the Division of Integrative Biosciences and Biotechnology and
- Department of Life Sciences, Pohang University of Science and Technology, Pohang, Gyeongbuk 37673, Republic of Korea
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5
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Kung CP, Maggi LB, Weber JD. The Role of RNA Editing in Cancer Development and Metabolic Disorders. Front Endocrinol (Lausanne) 2018; 9:762. [PMID: 30619092 PMCID: PMC6305585 DOI: 10.3389/fendo.2018.00762] [Citation(s) in RCA: 57] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/30/2018] [Accepted: 12/03/2018] [Indexed: 12/26/2022] Open
Abstract
Numerous human diseases arise from alterations of genetic information, most notably DNA mutations. Thought to be merely the intermediate between DNA and protein, changes in RNA sequence were an afterthought until the discovery of RNA editing 30 years ago. RNA editing alters RNA sequence without altering the sequence or integrity of genomic DNA. The most common RNA editing events are A-to-I changes mediated by adenosine deaminase acting on RNA (ADAR), and C-to-U editing mediated by apolipoprotein B mRNA editing enzyme, catalytic polypeptide 1 (APOBEC1). Both A-to-I and C-to-U editing were first identified in the context of embryonic development and physiological homeostasis. The role of RNA editing in human disease has only recently started to be understood. In this review, the impact of RNA editing on the development of cancer and metabolic disorders will be examined. Distinctive functions of each RNA editase that regulate either A-to-I or C-to-U editing will be highlighted in addition to pointing out important regulatory mechanisms governing these processes. The potential of developing novel therapeutic approaches through intervention of RNA editing will be explored. As the role of RNA editing in human disease is elucidated, the clinical utility of RNA editing targeted therapies will be needed. This review aims to serve as a bridge of information between past findings and future directions of RNA editing in the context of cancer and metabolic disease.
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Affiliation(s)
- Che-Pei Kung
- ICCE Institute, Washington University School of Medicine, Saint Louis, MO, United States
- Division of Molecular Oncology, Department of Medicine, Washington University School of Medicine, Saint Louis, MO, United States
| | - Leonard B. Maggi
- ICCE Institute, Washington University School of Medicine, Saint Louis, MO, United States
- Division of Molecular Oncology, Department of Medicine, Washington University School of Medicine, Saint Louis, MO, United States
| | - Jason D. Weber
- ICCE Institute, Washington University School of Medicine, Saint Louis, MO, United States
- Division of Molecular Oncology, Department of Medicine, Washington University School of Medicine, Saint Louis, MO, United States
- Siteman Cancer Center, Department of Cell Biology and Physiology, Washington University School of Medicine, Saint Louis, MO, United States
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6
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Kulkarni S, Ramsuran V, Rucevic M, Singh S, Lied A, Kulkarni V, O'hUigin C, Le Gall S, Carrington M. Posttranscriptional Regulation of HLA-A Protein Expression by Alternative Polyadenylation Signals Involving the RNA-Binding Protein Syncrip. THE JOURNAL OF IMMUNOLOGY 2017; 199:3892-3899. [PMID: 29055006 DOI: 10.4049/jimmunol.1700697] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/11/2017] [Accepted: 09/25/2017] [Indexed: 01/15/2023]
Abstract
Genomic variation in the untranslated region (UTR) has been shown to influence HLA class I expression level and associate with disease outcomes. Sequencing of the 3'UTR of common HLA-A alleles indicated the presence of two polyadenylation signals (PAS). The proximal PAS is conserved, whereas the distal PAS is disrupted within certain alleles by sequence variants. Using 3'RACE, we confirmed expression of two distinct forms of the HLA-A 3'UTR based on use of either the proximal or the distal PAS, which differ in length by 100 bp. Specific HLA-A alleles varied in the usage of the proximal versus distal PAS, with some alleles using only the proximal PAS, and others using both the proximal and distal PAS to differing degrees. We show that the short and the long 3'UTR produced similar mRNA expression levels. However, the long 3'UTR conferred lower luciferase activity as compared with the short form, indicating translation inhibition of the long 3'UTR. RNA affinity pull-down followed by mass spectrometry analysis as well as RNA coimmunoprecipitation indicated differential binding of Syncrip to the long versus short 3'UTR. Depletion of Syncrip by small interfering RNA increased surface expression of an HLA-A allotype that uses primarily the long 3'UTR, whereas an allotype expressing only the short form was unaffected. Furthermore, specific blocking of the proximal 3'UTR reduced surface expression without decreasing mRNA expression. These data demonstrate HLA-A allele-specific variation in PAS usage, which modulates their cell surface expression posttranscriptionally.
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Affiliation(s)
- Smita Kulkarni
- Ragon Institute of MGH, MIT and Harvard, Cambridge, MA 02139; .,Department of Genetics, Texas Biomedical Research Institute, San Antonio, TX 78227
| | - Veron Ramsuran
- Ragon Institute of MGH, MIT and Harvard, Cambridge, MA 02139.,Cancer and Inflammation Program, Leidos Biomedical Research Inc., Frederick National Laboratory for Cancer Research, Frederick, MD 21702.,KwaZulu-Natal Research Innovation and Sequencing Platform, School of Laboratory Medicine and Medical Sciences, University of KwaZulu-Natal, Durban 4001, South Africa.,Centre for the AIDS Programme of Research in South Africa, Nelson R. Mandela School of Medicine, University of KwaZulu-Natal, Durban 4001, South Africa; and
| | | | - Sukhvinder Singh
- Department of Genetics, Texas Biomedical Research Institute, San Antonio, TX 78227
| | - Alexandra Lied
- Ragon Institute of MGH, MIT and Harvard, Cambridge, MA 02139
| | - Viraj Kulkarni
- Ragon Institute of MGH, MIT and Harvard, Cambridge, MA 02139.,Department of Virology and Immunology, Texas Biomedical Research Institute, San Antonio, TX 78227
| | - Colm O'hUigin
- Cancer and Inflammation Program, Leidos Biomedical Research Inc., Frederick National Laboratory for Cancer Research, Frederick, MD 21702
| | - Sylvie Le Gall
- Ragon Institute of MGH, MIT and Harvard, Cambridge, MA 02139
| | - Mary Carrington
- Ragon Institute of MGH, MIT and Harvard, Cambridge, MA 02139.,Cancer and Inflammation Program, Leidos Biomedical Research Inc., Frederick National Laboratory for Cancer Research, Frederick, MD 21702
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7
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Severi F, Conticello SG. Flow-cytometric visualization of C>U mRNA editing reveals the dynamics of the process in live cells. RNA Biol 2016; 12:389-97. [PMID: 25806564 PMCID: PMC4615904 DOI: 10.1080/15476286.2015.1026033] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
APOBEC1 is the catalytic subunit of the complex that edits ApolipoproteinB (ApoB) mRNA, which specifically deaminates cytidine 6666 to uracil in the human transcript. The editing leads to the generation of a stop codon, resulting in the synthesis of a truncated form of ApoB. We have developed a method to quantitatively assay ApoB RNA editing in live cells by using a double fluorescent mCherry-EGFP chimera containing a ∼300bp fragment encompassing the region of ApoB subject to RNA editing. Coexpression of APOBEC1 together with this chimera causes specific RNA editing of the ApoB fragment. The insertion of a stop codon between the mCherry and EGFP thus induces the loss of EGFP fluorescence. Using this method we analyze the dynamics of APOBEC1-dependent RNA editing under various conditions. Namely we show the interplay of APOBEC1 with known interactors (ACF, hnRNP-C1, GRY-RBP) in cells that are RNA editing-proficient (HuH-7) or -deficient (HEK-293T), and the effects of restricted cellular localization of APOBEC1 on the efficiency of the editing. Furthermore, our approach is effective in assaying the induction of RNA editing in Caco-2, a cellular model physiologically capable of ApoB RNA editing.
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Key Words
- ACF, APOBEC1 Complementation Factor
- ADAR, Adenosine Deaminase, RNA-specific
- ADAT, Adenosine Deaminase, tRNA-specific
- AID/APOBECs
- APOBEC1, Apolipoprotein B mRNA editing enzyme, catalytic polypeptide 1
- ApoB, Apolipoprotein B
- EGFP, Enhanced Green Fluorescent Protein
- FACS, Fluorescence activated cell sorting
- FBS, Fetal bovine serum
- GRY-RBP, Glycine-Arginine-Tyrosine-rich RNA-binding protein
- RBM47, RNA binding motif protein 47
- RNA editing
- cds, coding sequence
- cytosine deaminase
- hnRNP-C1, heterogeneous nuclear ribonucleoprotein C1
- lipid metabolism
- mRNA
- post-transcriptional modification
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Affiliation(s)
- Francesco Severi
- a Core Research Laboratory; Istituto Toscano Tumori ; Firenze , Italy
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8
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Stake M, Singh D, Singh G, Marcela Hernandez J, Kaddis Maldonado R, Parent LJ, Boris-Lawrie K. HIV-1 and two avian retroviral 5' untranslated regions bind orthologous human and chicken RNA binding proteins. Virology 2015; 486:307-20. [PMID: 26584240 DOI: 10.1016/j.virol.2015.06.001] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2015] [Revised: 05/31/2015] [Accepted: 06/01/2015] [Indexed: 01/12/2023]
Abstract
Essential host cofactors in retrovirus replication bind cis-acting sequences in the 5'untranslated region (UTR). Although host RBPs are crucial to all aspects of virus biology, elucidating their roles in replication remains a challenge to the field. Here RNA affinity-coupled-proteomics generated a comprehensive, unbiased inventory of human and avian RNA binding proteins (RBPs) co-isolating with 5'UTRs of HIV-1, spleen necrosis virus and Rous sarcoma virus. Applying stringent biochemical and statistical criteria, we identified 185 RBP; 122 were previously implicated in retrovirus biology and 63 are new to the 5'UTR proteome. RNA electrophoretic mobility assays investigated paralogs present in the common ancestor of vertebrates and one hnRNP was identified as a central node to the biological process-anchored networks of HIV-1, SNV, and RSV 5' UTR-proteomes. This comprehensive view of the host constituents of retroviral RNPs is broadly applicable to investigation of viral replication and antiviral response in both human and avian cell lineages.
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Affiliation(s)
- Matthew Stake
- Department of Medicine, Penn State College of Medicine, 500 University Drive, Hershey, PA 17033, USA.
| | - Deepali Singh
- School of Biotechnology, Gautam Buddha University, Greater Noida, 201312, India.
| | - Gatikrushna Singh
- Department Veterinary & Biomedical Sciences, University of Minnesota, 205 VSB, 1971 Commonwealth Avenue, Saint Paul, MN 55108.
| | - J Marcela Hernandez
- Department of Veterinary Biosciences, Center for Retrovirus Research, Center for RNA Biology, Comprehensive Cancer Center, Ohio State University, Columbus, OH, USA.
| | - Rebecca Kaddis Maldonado
- Department of Medicine, Penn State College of Medicine, 500 University Drive, Hershey, PA 17033, USA.
| | - Leslie J Parent
- Department of Medicine, Penn State College of Medicine, 500 University Drive, Hershey, PA 17033, USA; Department Microbiology & Immunology, Penn State College of Medicine, 500 University Drive, Hershey, PA 17033, USA.
| | - Kathleen Boris-Lawrie
- Department Veterinary & Biomedical Sciences, University of Minnesota, 205 VSB, 1971 Commonwealth Avenue, Saint Paul, MN 55108.
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9
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Abstract
Cytidine (C) to Uridine (U) RNA editing is a post-trancriptional modification that until recently was known to only affect Apolipoprotein b (Apob) RNA and minimally require 2 components of the C to U editosome, the deaminase APOBEC1 and the RNA-binding protein A1CF. Our latest work has identified a novel RNA-binding protein, RBM47, as a core component of the editosome, which can substitute A1CF for the editing of ApoB mRNA. In addition, new RNA species that are subjected to C to U editing have been identified. Here, we highlight these recent discoveries and discuss how they change our view of the composition of the C to U editing machinery and expand our knowledge of the functional attributes of C to U RNA editing.
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Affiliation(s)
- Nicolas Fossat
- a Embryology Unit; Children's Medical Research Institute ; Westmead , Australia
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10
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Abstract
microRNAs constitute a large family of approximately 21-nucleotide-long, noncoding RNAs. They emerged more than 20 years ago as key posttranscriptional regulators of gene expression. The regulatory role of these small RNA molecules has recently begun to be explored in the human reproductive system. microRNAs have been shown to play an important role in control of reproductive functions, especially in the processes of oocyte maturation, folliculogenesis, corpus luteum function, implantation, and early embryonic development. Knockout of Dicer, the cytoplasmic enzyme that cleaves the pre-miRNA to its mature form, results in postimplantation embryonic lethality in several animal models, attributing to these small RNA vital functions in reproduction and development. Another intriguing characteristic of microRNAs is their presence in body fluids in a remarkably stable form that is protected from endogenous RNase activity. In this chapter we will describe the current knowledge on microRNAs, specifically relating to human gonadal cells. We will focus on their role in the ovarian physiologic process and ovulation dysfunction, regulation of spermatogenesis and male fertility, and putative involvement in human normal and aberrant trophoblast differentiation and invasion through the process of placentation.
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11
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Wigington CP, Williams KR, Meers MP, Bassell GJ, Corbett AH. Poly(A) RNA-binding proteins and polyadenosine RNA: new members and novel functions. WILEY INTERDISCIPLINARY REVIEWS. RNA 2014; 5:601-22. [PMID: 24789627 PMCID: PMC4332543 DOI: 10.1002/wrna.1233] [Citation(s) in RCA: 60] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/23/2013] [Revised: 02/07/2014] [Accepted: 03/06/2014] [Indexed: 02/05/2023]
Abstract
Poly(A) RNA-binding proteins (Pabs) bind with high affinity and specificity to polyadenosine RNA. Textbook models show a nuclear Pab, PABPN1, and a cytoplasmic Pab, PABPC, where the nuclear PABPN1 modulates poly(A) tail length and the cytoplasmic PABPC stabilizes poly(A) RNA in the cytoplasm and also enhances translation. While these conventional roles are critically important, the Pab family has expanded recently both in number and in function. A number of novel roles have emerged for both PAPBPN1 and PABPC that contribute to the fine-tuning of gene expression. Furthermore, as the characterization of the nucleic acid binding properties of RNA-binding proteins advances, additional proteins that show high affinity and specificity for polyadenosine RNA are being discovered. With this expansion of the Pab family comes a concomitant increase in the potential for Pabs to modulate gene expression. Further complication comes from an expansion of the potential binding sites for Pab proteins as revealed by an analysis of templated polyadenosine stretches present within the transcriptome. Thus, Pabs could influence mRNA fate and function not only by binding to the nontemplated poly(A) tail but also to internal stretches of adenosine. Understanding the diverse functions of Pab proteins is not only critical to understand how gene expression is regulated but also to understand the molecular basis for tissue-specific diseases that occur when Pab proteins are altered. Here we describe both conventional and recently emerged functions for PABPN1 and PABPC and then introduce and discuss three new Pab family members, ZC3H14, hnRNP-Q1, and LARP4.
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Affiliation(s)
- Callie P. Wigington
- Department of Biochemistry, Emory University School of Medicine, Atlanta, GA, USA
| | - Kathryn R. Williams
- Department of Cell Biology, Emory University School of Medicine, Atlanta, GA, USA
| | - Michael P. Meers
- Curriculum in Genetics and Molecular Biology, University of North Carolina, Chapel Hill, NC, USA
| | - Gary J. Bassell
- Department of Cell Biology, Emory University School of Medicine, Atlanta, GA, USA
| | - Anita H. Corbett
- Department of Biochemistry, Emory University School of Medicine, Atlanta, GA, USA
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12
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Shimizu Y, Nishitsuji H, Marusawa H, Ujino S, Takaku H, Shimotohno K. The RNA-editing enzyme APOBEC1 requires heterogeneous nuclear ribonucleoprotein Q isoform 6 for efficient interaction with interleukin-8 mRNA. J Biol Chem 2014; 289:26226-26238. [PMID: 25100733 DOI: 10.1074/jbc.m114.563221] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Apolipoprotein B mRNA-editing enzyme, catalytic polypeptide 1 (APOBEC1) is an intestine-specific RNA-binding protein. However, inflammation or exposure to DNA-damaging agents can induce ectopic APOBEC1 expression, which can result in hepatocellular hyperplasia in animal models. To identify its RNA targets, FLAG-tagged APOBEC1 was immunoprecipitated from transfected HuH7.5 hepatocellular carcinoma cells and analyzed using DNA microarrays. The interleukin-8 (IL8) mRNA was the most abundant co-precipitated RNA. Exogenous APOBEC1 expression increased IL8 production by extending the half-life of the IL8 mRNA. A cluster of AU-rich elements in the 3'-UTR of IL8 was essential to the APOBEC1-mediated increase in IL8 production. Notably, IL8 mRNA did not co-immunoprecipitate with APOBEC1 from lysates of other cell types at appreciable levels; therefore, other factors may enhance the association between APOBEC1 and IL8 mRNA in a cell type-specific manner. A yeast two-hybrid analysis and siRNA screen were used to identify proteins that enhance the interaction between APOBEC1 and IL8 mRNA. Heterogeneous nuclear ribonucleoprotein Q (hnRNPQ) was essential to the APOBEC1/IL8 mRNA association in HuH7.5 cells. Of the seven hnRNPQ isoforms, only hnRNPQ6 enabled APOBEC1 to bind to IL8 mRNA when overexpressed in HEK293 cells, which expressed the lowest level of endogenous hnRNPQ6 among the cell types examined. The results of a reporter assay using a luciferase gene fused to the IL8 3'-UTR were consistent with the hypothesis that hnRNPQ6 is required for APOBEC1-enhanced IL8 production. Collectively, these data indicate that hnRNPQ6 promotes the interaction of APOBEC1 with IL8 mRNA and the subsequent increase in IL8 production.
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Affiliation(s)
- Yuko Shimizu
- Research Center for Hepatitis and Immunology, National Center for Global Health and Medicine, 1-7-1, Kohnodai, Ichikawa, Chiba 272-8516, Japan,.
| | - Hironori Nishitsuji
- Research Center for Hepatitis and Immunology, National Center for Global Health and Medicine, 1-7-1, Kohnodai, Ichikawa, Chiba 272-8516, Japan
| | - Hiroyuki Marusawa
- Department of Gastroenterology and Hepatology, Graduate School of Medicine, Kyoto University, 54, Kawaramachi, Shogoin, Sakyo-ku, Kyoto 606-8507, Japan, and
| | - Saneyuki Ujino
- Research Center for Hepatitis and Immunology, National Center for Global Health and Medicine, 1-7-1, Kohnodai, Ichikawa, Chiba 272-8516, Japan
| | - Hiroshi Takaku
- Department of Life and Environmental Sciences, Chiba Institute of Technology, 2-17-1 Tsudanuma, Narashino, Chiba 275-0016, Japan
| | - Kunitada Shimotohno
- Research Center for Hepatitis and Immunology, National Center for Global Health and Medicine, 1-7-1, Kohnodai, Ichikawa, Chiba 272-8516, Japan
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13
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Imbar T, Eisenberg I. Regulatory role of microRNAs in ovarian function. Fertil Steril 2014; 101:1524-30. [DOI: 10.1016/j.fertnstert.2014.04.024] [Citation(s) in RCA: 88] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2014] [Revised: 04/13/2014] [Accepted: 04/15/2014] [Indexed: 01/08/2023]
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14
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Galloway CA, Ashton J, Sparks JD, Mooney RA, Smith HC. Metabolic regulation of APOBEC-1 complementation factor trafficking in mouse models of obesity and its positive correlation with the expression of ApoB protein in hepatocytes. Biochim Biophys Acta Mol Basis Dis 2010; 1802:976-85. [PMID: 20541607 DOI: 10.1016/j.bbadis.2010.06.003] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2010] [Revised: 06/03/2010] [Accepted: 06/03/2010] [Indexed: 10/19/2022]
Abstract
APOBEC-1 Complementation Factor (ACF) is an RNA-binding protein that interacts with apoB mRNA to support RNA editing. ACF traffics between the cytoplasm and nucleus. It is retained in the nucleus in response to elevated serum insulin levels where it supports enhanced apoB mRNA editing. In this report we tested whether ACF may have the ability to regulate nuclear export of apoB mRNA to the sites of translation in the cytoplasm. Using mouse models of obesity-induced insulin resistance and primary hepatocyte cultures we demonstrated that both nuclear retention of ACF and apoB mRNA editing were reduced in the livers of hyperinsulinemic obese mice relative to lean controls. Coincident with an increase in the recovery of ACF in the cytoplasm was an increase in the proportion of total cellular apoB mRNA recovered in cytoplasmic extracts. Cytoplasmic ACF from both lean controls and obese mouse livers was enriched in endosomal fractions associated with apoB mRNA translation and ApoB lipoprotein assembly. Inhibition of ACF export to the cytoplasm resulted in nuclear retention of apoB mRNA and reduced both intracellular and secreted ApoB protein in primary hepatocytes. The importance of ACF for modulating ApoB was supported by the finding that RNAi knockdown of ACF reduced ApoB secretion. An additional discovery from this study was the finding that leptin is a suppressor ACF expression. Dyslipidemia is a common pathology associated with insulin resistance that is in part due to the loss of insulin controlled secretion of lipid in ApoB-containing very low density lipoproteins. The data from animal models suggested that loss of insulin regulated ACF trafficking and leptin regulated ACF expression may make an early contribution to the overall pathology associated with very low density lipoprotein secretion from the liver in obese individuals.
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Affiliation(s)
- Chad A Galloway
- University of Rochester, Department of Biochemistry and Biophysics, 601 Elmwood Ave Rochester, NY 14642, USA
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15
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Quaresma AJ, Bressan G, Gava L, Lanza D, Ramos C, Kobarg J. Human hnRNP Q re-localizes to cytoplasmic granules upon PMA, thapsigargin, arsenite and heat-shock treatments. Exp Cell Res 2009; 315:968-80. [DOI: 10.1016/j.yexcr.2009.01.012] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2008] [Revised: 01/13/2009] [Accepted: 01/17/2009] [Indexed: 12/15/2022]
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16
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Barrandon C, Bonnet F, Nguyen VT, Labas V, Bensaude O. The transcription-dependent dissociation of P-TEFb-HEXIM1-7SK RNA relies upon formation of hnRNP-7SK RNA complexes. Mol Cell Biol 2007; 27:6996-7006. [PMID: 17709395 PMCID: PMC2168891 DOI: 10.1128/mcb.00975-07] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
The positive transcription elongation factor P-TEFb controls the elongation of transcription by RNA polymerase II. P-TEFb is inactivated upon binding to HEXIM1 or HEXIM2 proteins associated with a noncoding RNA, 7SK. In response to the inhibition of transcription, 7SK RNA, as well as HEXIM proteins, is released by an unknown mechanism and P-TEFb is activated. New partners of 7SK RNA were searched for as potential players in this feedback process. A subset of heterogeneous ribonuclear proteins, hnRNPs Q and R and hnRNPs A1 and A2, were thus identified as major 7SK RNA-associated proteins. The degree of association of 7SK RNA with these hnRNPs increased when P-TEFb-HEXIM1-7SK was dissociated following the inhibition of transcription or HEXIM1 knockdown. This finding suggested that 7SK RNA shuttles from HEXIM1-P-TEFb complexes to hnRNPs. The transcription-dependent dissociation of P-TEFb-HEXIM1-7SK complexes was attenuated when both hnRNPs A1 and A2 were knocked down by small interfering RNA. As hnRNPs are known to interact transiently with RNA while it is synthesized, hnRNPs released from nascent transcripts may trap 7SK RNA and thereby contribute to the activation of P-TEFb.
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Affiliation(s)
- Charlotte Barrandon
- UMR 8541 CNRS, Ecole Normale Supérieure, 46 rue d'Ulm, 75230 Paris Cedex 05, France
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17
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Chen Z, Eggerman TL, Patterson AP. ApoB mRNA editing is mediated by a coordinated modulation of multiple apoB mRNA editing enzyme components. Am J Physiol Gastrointest Liver Physiol 2007; 292:G53-65. [PMID: 16920700 DOI: 10.1152/ajpgi.00118.2006] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Apolipoprotein (apo)B mRNA editing is accomplished by a large multiprotein complex. How these proteins interact to achieve the precise single-nucleotide change induced by this complex remains unclear. We investigated the relationship between altered apoB mRNA editing and changes in editing enzyme components to evaluate their roles in editing regulation. In the mouse fetal small intestine, we found that the dramatic developmental upregulation of apoB mRNA editing from approximately 3% to 88% begins with decreased levels of inhibitory CUG binding protein 2 (CUGBP2) expression followed by increased levels of apoB mRNA editing enzyme (apobec)-1 and apobec-1 complementation factor (ACF) (4- and 8-fold) and then by decreased levels of the inhibitory components glycine-arginine-tyrosine-rich RNA binding protein (GRY-RBP) and heterogeneous nuclear ribonucleoprotein (hnRNP)-C1 (75% and 56%). In contrast, the expression of KH-type splicing regulatory protein (KSRP), apobec-1 binding protein (ABBP)1, ABBP2, and Bcl-2-associated athanogene 4 (BAG4) were unaltered. In the human intestinal cell line Caco-2, the increase of apoB mRNA editing from approximately 1.7% to approximately 23% was associated with 6- and 3.2-fold increases of apobec-1 and CUGBP2, respectively. In the mouse large intestine, the editing was 48% and had a 2.7-fold relatively greater CUGBP2 level. Caco-2 and the large intestine thus have increased instead of decreased CUGBP2 and a lower level of editing, suggesting that inhibitory CUGBP2 may play a critical role in the magnitude of editing regulation. Short interfering RNA-mediated gene-specific knockdown of CUGBP2, GRY-RBP, and hnRNP-C1 resulted in increased editing in Caco-2 cells, consistent with their known inhibitory function. These data suggest that a coordinated expression of editing components determines the magnitude and specificity of apoB mRNA editing.
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Affiliation(s)
- Zhigang Chen
- Office of Biotechnology Activities, National Institutes of Health, 6705 Rockledge Dr., Suite 750, Bethesda, MD 20892, USA
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18
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Smith HC. Measuring editing activity and identifying cytidine-to-uridine mRNA editing factors in cells and biochemical isolates. Methods Enzymol 2007; 424:389-416. [PMID: 17662851 DOI: 10.1016/s0076-6879(07)24018-2] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Cytidine deaminases with the capacity to act on nucleic acids play a critical role in regulating the proteome through diversification of expressed sequence beyond that encoded in the genome. A family of these enzymes, known as the APOBEC family of cytidine deaminases, has been identified in mammalian cells. APOBEC-1 edits messenger RNA, whereas other family members affect mRNA coding capacity by editing single-stranded DNA in expressed regions of the genomes. Biochemical isolation and analysis of APOBEC proteins and their interacting factors have led to an understanding of the diverse cellular processes including lipoprotein metabolism, antibody production, viral infectivity, and cancer. Practical approaches will be described for the measurement of editing activity and the analysis of proteins involved in C-to-U and dC-to-dU editing.
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Affiliation(s)
- Harold C Smith
- Department of Biochemistry, University of Rochester School of Medicine and Dentistry, Rochester, New York, USA
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19
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Kozak SL, Marin M, Rose KM, Bystrom C, Kabat D. The Anti-HIV-1 Editing Enzyme APOBEC3G Binds HIV-1 RNA and Messenger RNAs That Shuttle between Polysomes and Stress Granules. J Biol Chem 2006; 281:29105-19. [PMID: 16887808 DOI: 10.1074/jbc.m601901200] [Citation(s) in RCA: 149] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Deoxycytidine deaminases APOBEC3G (A3G) and APOBEC3F (A3F) (members of the apolipoprotein B mRNA-editing catalytic polypeptide 3 family) have RNA-binding motifs, invade assembling human immunodeficiency virus (HIV-1), and hypermutate reverse transcripts. Antagonistically, HIV-1 viral infectivity factor degrades these enzymes. A3G is enzymatically inhibited by binding RNA within an unidentified large cytosolic ribonucleoprotein, implying that RNA degradation during reverse transcription may activate intravirion A3G at the necessary moment. We purified a biologically active tandem affinity-tagged A3G from human HEK293T cells. Mass spectrometry and coimmunoprecipitation from HEK293T and T lymphocyte extracts identified many RNA-binding proteins specifically associated with A3G and A3F, including poly(A)-binding proteins (PABPs), YB-1, Ro-La, RNA helicases, ribosomal proteins, and Staufen1. Most strikingly, nearly all A3G-associated proteins were known to bind exclusively or intermittently to translating and/or dormant mRNAs. Accordingly, A3G in HEK293T and T lymphocyte extracts was almost completely in A3G-mRNA-PABP complexes that shifted reversibly between polysomes and dormant pools in response to translational inhibitors. For example arsenite, which inhibits 5'-cap-dependent translational initiation, shifted mRNA-A3G-PABP from polysomes into stress granules in a manner that was blocked and reversed by the elongation inhibitor cycloheximide. Immunofluorescence microscopy showed A3G-mRNA-PABP stress granules only partially overlapping with Staufen1. A3G coimmunoprecipitated HIV-1 RNA and many mRNAs. Ribonuclease released nearly all A3G-associated proteins, including A3G homo-oligomers and A3G-A3F hetero-oligomers, but the viral infectivity factor remained bound. Many proteins and RNAs associated with A3G are excluded from A3G-containing virions, implying that A3G competitively partitions into virions based on affinity for HIV-1 RNA.
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Affiliation(s)
- Susan L Kozak
- Department of Biochemistry and Molecular Biology and Proteomics Shared Resource, Oregon Health and Science University, Portland, Oregon 97239, USA
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20
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Passos DO, Quaresma AJC, Kobarg J. The methylation of the C-terminal region of hnRNPQ (NSAP1) is important for its nuclear localization. Biochem Biophys Res Commun 2006; 346:517-25. [PMID: 16765914 DOI: 10.1016/j.bbrc.2006.05.152] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2006] [Accepted: 05/21/2006] [Indexed: 11/19/2022]
Abstract
Protein arginine methylation is an irreversible post-translational protein modification catalyzed by a family of at least nine different enzymes entitled PRMTs (protein arginine methyl transferases). Although PRMT1 is responsible for 85% of the protein methylation in human cells, its substrate spectrum has not yet been fully characterized nor are the functional consequences of methylation for the protein substrates well understood. Therefore, we set out to employ the yeast two-hybrid system in order to identify new substrate proteins for human PRMT1. We were able to identify nine different PRMT1 interacting proteins involved in different aspects of RNA metabolism, five of which had been previously described either as substrates for PRMT1 or as functionally associated with PRMT1. Among the four new identified possible protein substrates was hnRNPQ3 (NSAP1), a protein whose function has been implicated in diverse steps of mRNA maturation, including splicing, editing, and degradation. By in vitro methylation assays we were able to show that hnRNPQ3 is a substrate for PRMT1 and that its C-terminal RGG box domain is the sole target for methylation. By further studies with the inhibitor of methylation Adox we provide evidence that hnRNPQ1-3 are methylated in vivo. Finally, we demonstrate by immunofluorescence analysis of HeLa cells that the methylation of hnRNPQ is important for its nuclear localization, since Adox treatment causes its re-distribution from the nucleus to the cytoplasm.
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Affiliation(s)
- Dario O Passos
- Centro de Biologia Molecular Estrutural, Laboratório Nacional de Luz Síncrotron, Campinas, SP, Brazil
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21
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Elvira G, Wasiak S, Blandford V, Tong XK, Serrano A, Fan X, del Rayo Sánchez-Carbente M, Servant F, Bell AW, Boismenu D, Lacaille JC, McPherson PS, DesGroseillers L, Sossin WS. Characterization of an RNA granule from developing brain. Mol Cell Proteomics 2005; 5:635-51. [PMID: 16352523 DOI: 10.1074/mcp.m500255-mcp200] [Citation(s) in RCA: 218] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In brain, mRNAs are transported from the cell body to the processes, allowing for local protein translation at sites distant from the nucleus. Using subcellular fractionation, we isolated a fraction from rat embryonic day 18 brains enriched for structures that resemble amorphous collections of ribosomes. This fraction was enriched for the mRNA encoding beta-actin, an mRNA that is transported in dendrites and axons of developing neurons. Abundant protein components of this fraction, determined by tandem mass spectrometry, include ribosomal proteins, RNA-binding proteins, microtubule-associated proteins (including the motor protein dynein), and several proteins described only as potential open reading frames. The conjunction of RNA-binding proteins, transported mRNA, ribosomal machinery, and transporting motor proteins defines these structures as RNA granules. Expression of a subset of the identified proteins in cultured hippocampal neurons confirmed that proteins identified in the proteomics were present in neurites associated with ribosomes and mRNAs. Moreover many of the expressed proteins co-localized together. Time lapse video microscopy indicated that complexes containing one of these proteins, the DEAD box 3 helicase, migrated in dendrites of hippocampal neurons at the same speed as that reported for RNA granules. Although the speed of the granules was unchanged by activity or the neurotrophin brain-derived neurotrophic factor, brain-derived neurotrophic factor, but not activity, increased the proportion of moving granules. These studies define the isolation and composition of RNA granules expressed in developing brain.
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Affiliation(s)
- George Elvira
- Département de Biochimie, Université de Montréal, 2900 Edouard-Montpetit, Montreal, Quebec H3C3J7, Canada
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22
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Kinnaird JH, Maitland K, Walker GA, Wheatley I, Thompson FJ, Devaney E. HRP-2, a heterogeneous nuclear ribonucleoprotein, is essential for embryogenesis and oogenesis in Caenorhabditis elegans. Exp Cell Res 2004; 298:418-30. [PMID: 15265690 DOI: 10.1016/j.yexcr.2004.04.043] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2004] [Revised: 04/20/2004] [Indexed: 11/17/2022]
Abstract
Heterogeneous nuclear ribonucleoproteins (hnRNPs) have fundamental roles in the posttranscriptional control of gene expression. Here, we describe an hnRNP from Caenorhabditis elegans(HRP-2), which shares significant homology with mammalian hnRNP R, hnRNP Q and ACF, the essential complementation factor in ApoB mRNA editing. All four proteins possess a similar molecular architecture, with three closely linked RNA-binding domains and a C-terminus that contains RG/RGG repeat motifs. An HRP-2::GFP fusion protein was ubiquitously expressed in C. elegans during embryogenesis and subsequent larval development. Expression was also detected in the hermaphrodite gonad using a specific antibody, suggesting that HRP-2 is provided maternally. HRP-2 was predominantly localised to nuclei and analysis of transgenic lines expressing C-terminal deletions of HRP-2 defined a functional nuclear localisation signal. Analysis by RNAi demonstrated that HRP-2 was essential for embryogenesis and fertility. Cell divisions were slower in hrp-2(RNAi) embryos and the majority showed an early embryonic arrest phenotype. Shorter exposure to dsRNA allowed development to the twofold stage and the few embryos that hatched were abnormal. Adult worms that developed from embryos exposed to RNAi were completely sterile due to a failure in oocyte formation. These results demonstrate that HRP-2 or its RNA targets are essential for normal embryonic development and oogenesis in C. elegans.
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Affiliation(s)
- Jane H Kinnaird
- Veterinary Parasitology, Institute of Comparative Medicine, University of Glasgow, Glasgow G61 1QH, UK.
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23
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Rossoll W, Jablonka S, Andreassi C, Kröning AK, Karle K, Monani UR, Sendtner M. Smn, the spinal muscular atrophy-determining gene product, modulates axon growth and localization of beta-actin mRNA in growth cones of motoneurons. ACTA ACUST UNITED AC 2003; 163:801-12. [PMID: 14623865 PMCID: PMC2173668 DOI: 10.1083/jcb.200304128] [Citation(s) in RCA: 496] [Impact Index Per Article: 23.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Spinal muscular atrophy (SMA), a common autosomal recessive form of motoneuron disease in infants and young adults, is caused by mutations in the survival motoneuron 1 (SMN1) gene. The corresponding gene product is part of a multiprotein complex involved in the assembly of spliceosomal small nuclear ribonucleoprotein complexes. It is still not understood why reduced levels of the ubiquitously expressed SMN protein specifically cause motoneuron degeneration. Here, we show that motoneurons isolated from an SMA mouse model exhibit normal survival, but reduced axon growth. Overexpression of Smn or its binding partner, heterogeneous nuclear ribonucleoprotein (hnRNP) R, promotes neurite growth in differentiating PC12 cells. Reduced axon growth in Smn-deficient motoneurons correlates with reduced β-actin protein and mRNA staining in distal axons and growth cones. We also show that hnRNP R associates with the 3′ UTR of β-actin mRNA. Together, these data suggest that a complex of Smn with its binding partner hnRNP R interacts with β-actin mRNA and translocates to axons and growth cones of motoneurons.
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Affiliation(s)
- Wilfried Rossoll
- Institute for Clinical Neurobiology, University of Wuerzburg, 97080 Wuerzburg, Germany
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24
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Sowden MP, Lehmann DM, Lin X, Smith CO, Smith HC. Identification of novel alternative splice variants of APOBEC-1 complementation factor with different capacities to support apolipoprotein B mRNA editing. J Biol Chem 2003; 279:197-206. [PMID: 14570923 DOI: 10.1074/jbc.m307920200] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Two novel mRNA transcripts have been identified that result from species- and tissue-specific, alternative polyadenylation and splicing of the pre-mRNA encoding the apolipoprotein B (apoB) editing catalytic subunit 1 (APOBEC-1) complementation factor (ACF) family of related proteins. The alternatively processed mRNAs encode 43- and 45-kDa proteins that are components of the previously identified p44 cluster of apoB RNA binding, editosomal proteins. Recombinant ACF45 displaced ACF64 and ACF43 in mooring sequence RNA binding but did not demonstrate strong binding to APOBEC-1. In contrast, ACF43 bound strongly to APOBEC-1 but demonstrated weak binding to mooring sequence RNA. Consequently ACF45/43 complemented APOBEC-1 in apoB mRNA editing with less efficiency than full-length ACF64. These data, together with the finding that all ACF variants were co-expressed in rat liver nuclei (the site of apoB mRNA editing), suggested that ACF variants might compete with one another for APOBEC-1 and apoB mRNA binding and thereby contribute to the regulation of apoB mRNA editing. In support for this hypothesis, the ratio of nuclear ACF65/64 to ACF45/43 decreased when hepatic editing was inhibited by fasting and increased when editing was re-stimulated by refeeding. These findings suggested a new model for the regulation of apoB mRNA editing in which the catalytic potential of editosomes is modulated at the level of their assembly by alterations in the relative abundance of multiple related RNA-binding auxiliary proteins and the expression level of APOBEC-1.
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Affiliation(s)
- Mark P Sowden
- Department of Biochemistry and Biophysics, University of Rochester, NY 14642, USA
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25
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Lau PP, Chan L. Involvement of a chaperone regulator, Bcl2-associated athanogene-4, in apolipoprotein B mRNA editing. J Biol Chem 2003; 278:52988-96. [PMID: 14559896 DOI: 10.1074/jbc.m310153200] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Apobec-1 is the catalytic subunit of a multicomponent editosome complex that mediates apolipoprotein B (apoB) mRNA editing. We isolated a novel apobec-1-interacting protein by yeast two-hybrid cloning and identified the protein as BAG-4. BAG-4, a chaperone-regulating protein, also known as SODD (silencer of death domains), is a member of the BAG family of proteins. In this report, we found that apobec-1 is localized in the perinucleolar compartment in HepG2 cells and rat liver MCR-RH7777 cells. BAG-4 binds to apobec-1 via its N-terminal region independent of the BAG domain. It is ubiquitously expressed with predominant occurrence in human pancreas, heart, brain, and placenta. Immunoprecipitation experiments confirmed that BAG-4 interacts with Hsc70/Hsp90 in HepG2 cells. BAG-4 tagged with green fluorescent protein (GFP) or FLAG was localized both in cytoplasm of mouse BNLCL.2 liver cells and human liver hepatoma HepG2 cells. After heat shock, GFP-BAG-4 co-localizes with Hsc70 in the nucleus in HepG2 cells, whereas GFP-BAG-4 mutants lacking the BAG domain remain perinuclear. BAG-4 has no effects on apoB mRNA editing in vitro. However, unlike other apobec-1 complementation factors studied to date, antisense knockdown of BAG-4 in BNLCL.2 cells and in MCR-RH7777 cells increases rather than decreases endogenous apoB mRNA editing. Overexpression of BAG-4 in MCR-RH7777 cells also suppresses apoB mRNA editing. ApoB-48 production also increases with antisense BAG-4 expression in MCR-RH7777 cells. We previously showed that apoB mRNA editing is an intranuclear event (Lau, P. P., Xiong, W. J., Zhu, H. J., Chen, S. H., and Chan, L. (1991) J. Biol. Chem. 266, 20550-20554). Thus, BAG-4 overexpression down-regulates apoB mRNA editing by shuttling apobec-1 from the intranuclear perinucleolar compartment to the cytoplasm. We propose that BAG-4 functions as a negative regulator for apobec-1-mediated apoB mRNA editing through its ability to suppress the Hsp/Hsc70 chaperone activity and thereby editosome formation and, as a consequence, prevents nuclear localization of the apobec-1 editosome.
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Affiliation(s)
- Paul P Lau
- Department of Medicine, Baylor College of Medicine, Houston, Texas 77030, USA
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Fomenkov A, Huang YP, Topaloglu O, Brechman A, Osada M, Fomenkova T, Yuriditsky E, Trink B, Sidransky D, Ratovitski E. P63 alpha mutations lead to aberrant splicing of keratinocyte growth factor receptor in the Hay-Wells syndrome. J Biol Chem 2003; 278:23906-14. [PMID: 12692135 DOI: 10.1074/jbc.m300746200] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
p63, a p53 family member, is required for craniofacial and limb development as well as proper skin differentiation. However, p63 mutations associated with the ankyloblepharon-ectodermal dysplasia-clefting (AEC) syndrome (Hay-Wells syndrome) were found in the p63 carboxyl-terminal region with a sterile alpha-motif. By two-hybrid screen we identified several proteins that interact with the p63alpha carboxyl terminus and its sterile alpha-motif, including the apobec-1-binding protein-1 (ABBP1). AEC-associated mutations completely abolished the physical interaction between ABBP1 and p63alpha. Moreover the physical association of p63alpha and ABBP1 led to a specific shift of FGFR-2 alternative splicing toward the K-SAM isoform essential for epithelial differentiation. We thus propose that a p63alpha-ABBP1 complex differentially regulates FGFR-2 expression by supporting alternative splicing of the K-SAM isoform of FGFR-2. The inability of mutated p63alpha to support this splicing likely leads to the inhibition of epithelial differentiation and, in turn, accounts for the AEC phenotype.
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Affiliation(s)
- Alexey Fomenkov
- Department of Dermatology, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA
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Wedekind JE, Dance GSC, Sowden MP, Smith HC. Messenger RNA editing in mammals: new members of the APOBEC family seeking roles in the family business. Trends Genet 2003; 19:207-16. [PMID: 12683974 DOI: 10.1016/s0168-9525(03)00054-4] [Citation(s) in RCA: 233] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Alteration of mRNA sequence through base modification mRNA editing frequently generates protein diversity. Several proteins have been identified as being similar to C-to-U mRNA editing enzymes based on their structural domains and the occurrence of a catalytic domain characteristic of cytidine deaminases. In light of the hypothesis that these proteins might represent novel mRNA editing systems that could affect proteome diversity, we consider their structure, expression and relevance to biomedically significant processes or pathologies.
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Affiliation(s)
- Joseph E Wedekind
- Department of Biochemistry and Biophysics, University of Rochester, School of Medicine and Dentistry, 601 Elmwood Avenue, Rochester, NY 14623, USA
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28
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Affiliation(s)
- Valerie Blanc
- Department of Internal Medicine, Washington University School of Medicine, St. Louis, Missouri 63110, USA
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Carty SM, Greenleaf AL. Hyperphosphorylated C-terminal repeat domain-associating proteins in the nuclear proteome link transcription to DNA/chromatin modification and RNA processing. Mol Cell Proteomics 2002; 1:598-610. [PMID: 12376575 DOI: 10.1074/mcp.m200029-mcp200] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Using an interaction blot approach to search in the human nuclear proteome, we identified eight novel proteins that bind the hyperphosphorylated C-terminal repeat domain (phosphoCTD) of RNA polymerase II. Unexpectedly, five of the new phosphoCTD-associating proteins (PCAPs) represent either enzymes that act on DNA and chromatin (topoisomerase I, DNA (cytosine-5) methyltransferase 1, poly(ADP-ribose) polymerase-1) or proteins known to bind DNA (heterogeneous nuclear ribonucleoprotein (hnRNP) U/SAF-A, hnRNP D). The other three PCAPs represent factors involved in pre-mRNA metabolism as anticipated (CA150, NSAP1/hnRNP Q, hnRNP R) (note that hnRNP U/SAF-A and hnRNP D are also implicated in pre-mRNA metabolism). Identifying as PCAPs proteins involved in diverse DNA transactions suggests that the range of phosphoCTD functions extends far beyond just transcription and RNA processing. In view of the activities possessed by the DNA-directed PCAPs, it is likely that the phosphoCTD plays important roles in genome integrity, epigenetic regulation, and potentially nuclear structure. We present a model in which the phosphoCTD association of the PCAPs poises them to act either on the nascent transcript or on the DNA/chromatin template. We propose that the phosphoCTD of elongating RNA polymerase II is a major organizer of nuclear functions.
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Affiliation(s)
- Sherry M Carty
- Department of Biochemistry, Duke University Medical Center, Durham, North Carolina 27710, USA
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Sowden MP, Ballatori N, Jensen KLDM, Reed LH, Smith HC. The editosome for cytidine to uridine mRNA editing has a native complexity of 27S: identification of intracellular domains containing active and inactive editing factors. J Cell Sci 2002; 115:1027-39. [PMID: 11870221 DOI: 10.1242/jcs.115.5.1027] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Apolipoprotein B mRNA cytidine to uridine editing requires the assembly of a multiprotein editosome comprised minimally of the catalytic subunit,apolipoprotein B mRNA editing catalytic subunit 1 (APOBEC-1), and an RNA-binding protein, APOBEC-1 complementation factor (ACF). A rat homolog has been cloned with 93.5% identity to human ACF (huACF). Peptide-specific antibodies prepared against huACF immunoprecipitated a rat protein of similar mass as huACF bound to apolipoprotein B (apoB) RNA in UV cross-linking reactions, thereby providing evidence that the p66, mooring sequence-selective, RNA-binding protein identified previously in rat liver by UV cross-linking and implicated in editosome assembly is a functional homolog of huACF. The rat protein (p66/ACF) was distributed in both the nucleus and cytoplasm of rat primary hepatocytes. Within a thin section, a significant amount of total cellular p66/ACF was cytoplasmic, with a concentration at the outer surface of the endoplasmic reticulum. Native APOBEC-1 co-fractionated with p66/ACF in the cytoplasm as 60S complexes. In the nucleus, the biological site of apoB mRNA editing, native p66/ACF, was localized to heterochromatin and fractionated with APOBEC-1 as 27S editosomes. When apoB mRNA editing was stimulated in rat primary hepatocytes with ethanol or insulin, the abundance of p66/ACF in the nucleus markedly increased. It is proposed that the heterogeneity in size of complexes containing editing factors is functionally significant and reflects functionally engaged editosomes in the nucleus and an inactive cytoplasmic pool of factors.
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Affiliation(s)
- Mark P Sowden
- Department of Biochemistry and Biophysics, University of Rochester School of Medicine and Dentistry, Rochester, New York 14642, USA
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31
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Affiliation(s)
- Nicholas O Davidson
- Department of Internal Medicine, Washington University, St. Louis, Missouri 63110, USA.
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Blanc V, Henderson JO, Kennedy S, Davidson NO. Mutagenesis of apobec-1 complementation factor reveals distinct domains that modulate RNA binding, protein-protein interaction with apobec-1, and complementation of C to U RNA-editing activity. J Biol Chem 2001; 276:46386-93. [PMID: 11571303 DOI: 10.1074/jbc.m107654200] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
C to U editing of apolipoprotein B (apoB) RNA requires a multicomponent holoenzyme complex in which minimal constituents include apobec-1 and apobec-1 complementation factor (ACF). We have examined the predicted functional domains in ACF in binding apoB RNA, interaction with apobec-1, and complementation of RNA editing. We demonstrate that apoB RNA binding and apobec-1-interacting domains are defined by two partially overlapping regions containing the NH(2)-terminal RNA recognition motifs of ACF. Both apoB RNA binding and apobec-1 interaction are required for editing complementation activity. ACF is a nuclear protein that upon cotransfection with apobec-1 results in nuclear colocalization and redistribution of apobec-1 from the cytoplasm. ACF constructs with deletions or mutations in the putative nuclear localization signal (NLS) still localize in the nucleus of transfected cells but do not colocalize with apobec-1, the latter remaining predominantly cytoplasmic. These observations suggest that the putative NLS motif in ACF is not responsible for its nucleo-cytoplasmic trafficking. By contrast, protein-protein interaction is important for the nuclear import of apobec-1. Taken together, these data suggest that functional complementation of C to U RNA editing by apobec-1 involves the NH(2)-terminal 380 residues of ACF.
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Affiliation(s)
- V Blanc
- Department of Internal Medicine, Washington University School of Medicine, St. Louis, Missouri 63110, USA
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Lau PP, Villanueva H, Kobayashi K, Nakamuta M, Chang BH, Chan L. A DnaJ protein, apobec-1-binding protein-2, modulates apolipoprotein B mRNA editing. J Biol Chem 2001; 276:46445-52. [PMID: 11584023 DOI: 10.1074/jbc.m109215200] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Mammalian homologues of DnaJ proteins, also known as Hsp40 proteins, are co-chaperonins that complement Hsp70 chaperone function. Using the yeast two-hybrid system, we cloned an apolipoprotein (apo) B mRNA editing complementation protein, called apobec-1-binding protein-2 (ABBP-2), and found that it is a Class II DnaJ homologue. ABBP-2 binds to apobec-1, the mammalian apoB mRNA editase, via its J domain and neighboring G/F domain. It is a ubiquitously expressed protein, and, by transfection analysis of GFP-ABBP-2, we found that the protein is located in both the nucleus and cytosol of transfected cells, with predominance in the nucleus. Down-regulation of ABBP-2 expression in cultured cells inhibits endogenous apobec-1-mediated apoB mRNA editing. Like other Hsp40 proteins, ABBP-2 binds to Hsp70 and has ATPase-stimulating activity. Apobec-1-mediated apoB mRNA editing activity of in vitro tissue extracts requires the presence of Hsp70/ABBP-2. Although exogenously added ATP is not required for editing activity, removal of the endogenous ATP present in these extracts, which disrupts ABBP-2-Hsp70 interaction, completely inhibits editing. ABBP-2 differs from previously described auxiliary proteins (ABBP-1, ACF, and GRY-RBP) in that it does not contain any RNA recognition motifs. Not only is ABBP-2 required for efficient apoB mRNA editing, this newly discovered apobec-1-binding protein may help determine the subcellular distribution and trafficking of apobec-1 via its interaction with the chaperonin Hsp70.
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Affiliation(s)
- P P Lau
- Department of Medicine, Baylor College of Medicine, Houston, Texas 77030, USA
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